1. Field of the Invention
The present invention relates to an image freezing signal-processing apparatus capable of forming a freeze image free from blurs.
2. Related Art Statement
Recently, the density of pixels has been raised and the size of the chip has been extremely reduced with an advancement of a solid state image sensing technology. As a result, an endoscope having, at its leading portion, a solid-state image sensing device, that is, so-called an electronic endoscope apparatus has been developed. An electronic endoscope apparatus of the type described above has a function of observing an inspection subject portion by inserting its insertion portion into the coelom and another function of recording the observed image of the subject portion. Therefore, the observing performance and the quality of the recorded image are very important to accurately diagnose the inspection subject portion. As a result, an operator of the endoscope must performs the recording operation in such a manner that an image of the inspection subject portion is freeze-displayed several times after a patient has been allowed to repose. Then, the optimum image is selected and, as a still picture, recorded to an apparatus for photographing the monitor image, a video printer, a still video floppy apparatus or the like. However, if the patient is allowed to repose, the inspection subject portion necessarily moves because the inspection subject portion is an organism. As a result, there arises a problem in that the freeze picture forming operation must be repeatedly performed in order to eliminate the image blurs due to the movement of the subject portion.
The above-described deterioration in the recorded image due to the movement of the subject takes place depending upon the type of the image sensing device and the image sensing method. For example, in a case where a frame-transfer type CCD (hereinafter called a "FT type CCD") is used as the image sensing device, the movement of the subject in the image exposure period causes the image deviation to be generated. In another case where an interline type CCD (hereinafter called an "IT type CCD") is used to perform a jump scanning operation, a flicker take place due to the image difference generated between the fields in addition to the above-described problem of image blurs, as described above, caused from the movement of the subjected in the image exposure period. Furthermore, a color plane sequence method, in which a monochromatic type CCD is attached to the leading portion of the endoscope for the purpose of reducing the diameter of the endoscope and, for example, RGB sequence light is used as illuminating light, encounters a problem in that the movement of the subject is displayed as the color misregistration because each of R, G and B original color images sequentially photographed in the time sequential manner are displayed after they have been made time-coincide. As a result, a problem of a so-called color misregistration takes place.
In order to overcome the above-described problems, the applicant of the present invention has disclosed an apparatus in Japanese Patent Application No. 1988-209677. According to this disclosure, the apparatus is arranged in such a manner that image blurs (color misregistration or the like) of each of image signals supplied in a certain time period is detected and an image signal displaying the minimum image blurs is displayed on a monitor or the like as a still picture in place of the conventional structure in which the still picture is displayed on a monitor or the like simultaneously with the commencement of the freezing operation.
However, an undesirable certain time lag is generated in the above-described apparatus disclosed in Japanese Patent Application No. 1988-209677 from the moment at which the freeze operation is performed to the moment at which the still picture is actually obtained. Therefore, an operator of the apparatus feels strange about the apparatus or an undesirable image is frozen.
It might be feasible to employ a structure of the type disclosed in Japanese Patent Application No. 1988-109187 and arranged in such a manner that a plurality of continuous image frames are recorded and an image free from the color misregistration is selected from a plurality of the image frames so as to be displayed. However, an apparatus of this type is disadvantageous in terms of cost and size reductions because a memory having a large capacity must be provided.